[postgis-users] Querying Multiple Rasters

Rémi Cura remi.cura at gmail.com
Wed Jul 31 00:51:05 PDT 2013 

Sorry for the double post.
One last thing :
about your query:
you do a ST_clip ( st_union )
You could try a ST_union(st_clip) .
If you have a lot of big rasters it may be faster (??).

Cheers,
Rémi-C

2013/7/31 Rémi Cura <remi.cura at gmail.com>

> Hey
> Sorry to bother you with technical details, but your query being slow may
> come from hardware, OS, postgres, postgis, bad partitionning, bad query,
> bad index,...
> So can you give more details please?
>
> What are your versions (OS,postgres, postgis, gdal).
> What is the on disk size of a child table (see statistics)
> How many rows are there in a child table?
> I'm guessing you have an index about envelope of each row.
>
> What says a EXPLAIN ANALYZE of your query ?
>
>
> Quick check list :
>
> Hardware
> [_] Have you two separate hard disk (one for sys, one for data) / Is your
> disk the bottleneck?
> OS
> [_] What is your system doing when computing a query (look for process,
> memory usage, disk usage)
> [_] Is you OS caching working?
> [_] if linux, have you tun your kernel max memory?
>
> Postgres
> [_] Have you tuned postgresql.conf conf (very restrictive by default :
> MUST DO).
> Postgis
> [_] ...no idea yet...
> Partitionning
> [_] Are your constraints on child table sufficently restrictive to avoid
> querrying a lots of child table
> [_] Are your constraints used by query planner (explain analyze) .
> If you want to be sure, you can manually explicit it for test purpose :
> adding to WHERE clause "AND st_coveredby(st_convexhull(rast), '*
> ...truncated...*'::geometry)) = TRUE
> Query
> [_] I'm guessing you test your query in pgadmin before using python : you
> could start from minimal query (find rasters in a clipping zone directly
> querying a child table), then make it grow (find rasters in father
> table,then  compute new raster from previous result, etc), watching how the
> processing time grows in the process.
> Also you should know the computational price of doing ST_AsGDALRaster(ST_CLIP(ST_Union(rast),
> that is separate the time to find "rast" intersecting your clipping zone,
> and the time to compute a union and the ST_AsGdalRaster function.
>
> [_] As suggested, and if you want to avoid sending another query first to
> compute our clipping box, you could use CTE (IE a "WITH" statement), or
> subquery. This way you avoid computing it twice :
> WITH my_clipping_geom AS (
> SELECT ST_Transform(ST_GeomFromText( wkt, map_srs,table_srs)) AS geom
> LIMIT 1
> )
> SELECT ST_AsGDALRaster(ST_CLIP(ST_Union(rast), my_clipping_geom.geom ,raster_type)
>
> FROM table_name, my_clipping_geom
> WHERE ST_Intersects(rast,my_clipping_geom.geom)
>
> Index
> [_] You use ST_Intersects, therefore you must have an index to speed it up.
> I'm guessing you have one on bounding box of each raster (each line), is
> it used (explain analyze : index scan)
>
> Don't lose hope, as the whole system can be severly speeded up by tuning
> and small change may have big effects.
>
> Cheers,
> Rémi-C
>
>
>
> 2013/7/30 Jayson Gallardo <jaysontrades at gmail.com>
>
>> Thanks for the help again. There will be extensive testing before we go
>> into production. Right now, we're just trying to get a prototype up and
>> running. I might need to look into querying a web service for clipped NED
>> data...
>>
>>
>> On Tue, Jul 30, 2013 at 12:01 PM, Bborie Park <dustymugs at gmail.com>wrote:
>>
>>> That should work if you're querying against the subparent instead of the
>>> parent. You'll need to test though...
>>>
>>> -bborie
>>>
>>>
>>> On Tue, Jul 30, 2013 at 9:59 AM, Jayson Gallardo <jaysontrades at gmail.com
>>> > wrote:
>>>
>>>> What if I create subparents for each state, and set an extent
>>>> constraint on each subparent? Would that help? Or would the query still
>>>> check the constraint for each child of each subparent?
>>>>
>>>>
>>>> On Tue, Jul 30, 2013 at 11:54 AM, Bborie Park <dustymugs at gmail.com>wrote:
>>>>
>>>>> 3m NED data doesn't exist for the continental US (at least from USGS).
>>>>> But if you were to do so, you could consider a different scheme...
>>>>>
>>>>> 1. All NED files are stored as out-db rasters
>>>>> 2. Each table is for one state, though in some situations you may want
>>>>> more than one table per state (e.g. Texas, California).
>>>>>
>>>>> That should help you keep the # of partitions to a minimum and reduce
>>>>> the size of each partition.
>>>>>
>>>>> -bborie
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Jul 30, 2013 at 9:42 AM, Jayson Gallardo <
>>>>> jaysontrades at gmail.com> wrote:
>>>>>
>>>>>> I was reading the page on partitioning, and the very last line says*"
>>>>>> **Partitioning using these techniques will work well with up to
>>>>>> perhaps a hundred partitions; don't try to use many thousands of
>>>>>> partitions." *I'm already up to ~400 tables in this partitioning
>>>>>> scheme just for Arkansas and Iowa... Is this a good idea? Would there be a
>>>>>> better way to do the entire continental US?
>>>>>>
>>>>>>
>>>>>> On Tue, Jul 30, 2013 at 11:39 AM, Bborie Park <dustymugs at gmail.com>wrote:
>>>>>>
>>>>>>> The quick and dirty approach is to have a query before that query
>>>>>>> that transforms the WKT.
>>>>>>>
>>>>>>> Something like "SELECT ST_AsEWKT(ST_Transform(...))"
>>>>>>>
>>>>>>> -bborie
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Jul 30, 2013 at 9:35 AM, Jayson Gallardo <
>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>
>>>>>>>> I suppose I could do that in my script. How should I go about that?
>>>>>>>> My process is as follows:
>>>>>>>>
>>>>>>>>    - User selects area of interest on a map (openlayers)
>>>>>>>>    - User clicks submit, and python script is called with the WKT
>>>>>>>>    passed as an argument
>>>>>>>>    - Python script queries the database, which then outputs the
>>>>>>>>    raster
>>>>>>>>    - Raster is processed through a library
>>>>>>>>    - Processed raster is displayed as an overlay on the map
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Jul 30, 2013 at 11:31 AM, Bborie Park <dustymugs at gmail.com>wrote:
>>>>>>>>
>>>>>>>>> Are you able to transform the wkt before passing it to the sql?
>>>>>>>>> Partitioning only works on constant values, not values that need
>>>>>>>>> processing, e.g. ST_Transform(ST_GeomFromText(\'%s\',%i),%i)).
>>>>>>>>>
>>>>>>>>> -bborie
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Tue, Jul 30, 2013 at 9:25 AM, Jayson Gallardo <
>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>
>>>>>>>>>> Here's the constraints:
>>>>>>>>>>   CONSTRAINT dem_elevation_n33w092_pkey PRIMARY KEY (rid ),
>>>>>>>>>>   CONSTRAINT enforce_height_rast CHECK (st_height(rast) = 100),
>>>>>>>>>>   CONSTRAINT enforce_max_extent_rast CHECK
>>>>>>>>>> (st_coveredby(st_convexhull(rast), '*...truncated...*
>>>>>>>>>> '::geometry)),
>>>>>>>>>>   CONSTRAINT enforce_num_bands_rast CHECK (st_numbands(rast) = 1),
>>>>>>>>>>   CONSTRAINT enforce_out_db_rast CHECK
>>>>>>>>>> (_raster_constraint_out_db(rast) = '{f}'::boolean[]),
>>>>>>>>>>   CONSTRAINT enforce_pixel_types_rast CHECK
>>>>>>>>>> (_raster_constraint_pixel_types(rast) = '{32BF}'::text[]),
>>>>>>>>>>   CONSTRAINT enforce_same_alignment_rast CHECK
>>>>>>>>>> (st_samealignment(rast, '*...truncated...*'::raster)),
>>>>>>>>>>   CONSTRAINT enforce_scalex_rast CHECK
>>>>>>>>>> (st_scalex(rast)::numeric(16,10) = 0.000092592592593::numeric(16,10)),
>>>>>>>>>>   CONSTRAINT enforce_scaley_rast CHECK
>>>>>>>>>> (st_scaley(rast)::numeric(16,10) = (-0.000092592592593)::numeric(16,10)),
>>>>>>>>>>   CONSTRAINT enforce_srid_rast CHECK (st_srid(rast) = 4269),
>>>>>>>>>>   CONSTRAINT enforce_width_rast CHECK (st_width(rast) = 100)
>>>>>>>>>>
>>>>>>>>>> and my python script:
>>>>>>>>>>
>>>>>>>>>> wkt = sys.argv[1]  # Polygon shape in WKT format
>>>>>>>>>> raster_type = 'GTiff'
>>>>>>>>>> table_name = 'dem_elevation'
>>>>>>>>>> map_srs = 900913
>>>>>>>>>> table_srs = 4269
>>>>>>>>>> sql_text = 'SELECT ST_AsGDALRaster(ST_CLIP(ST_Union(rast),
>>>>>>>>>> ST_GeomFromText(\'%s\',%i)),\'%s\') FROM "%s" WHERE
>>>>>>>>>> ST_Intersects(rast, ST_Transform(ST_GeomFromText(\'%s\',%i),%i))'
>>>>>>>>>>  % (wkt, map_srs, raster_type, table_name, wkt, map_srs,
>>>>>>>>>> table_srs)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Tue, Jul 30, 2013 at 11:12 AM, Bborie Park <
>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> Jayson,
>>>>>>>>>>>
>>>>>>>>>>> Can you share one of the queries? Also, what check constraints
>>>>>>>>>>> are you using?
>>>>>>>>>>>
>>>>>>>>>>> -bborie
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Tue, Jul 30, 2013 at 7:49 AM, Jayson Gallardo <
>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> So, I used Explain on my SELECT statement, and whether
>>>>>>>>>>>> constraint_exclusion is on or off, it seems to spit out the same number of
>>>>>>>>>>>> rows in the query plan. Is there something I need to do for my table
>>>>>>>>>>>> constraints so that it doesn't do a check on every table I have loaded?
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Jul 30, 2013 at 9:20 AM, Jayson Gallardo <
>>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> Quick follow up question to my situation... I recently loaded
>>>>>>>>>>>>> 3m resolution NED for Iowa. I have them loaded to one table per source
>>>>>>>>>>>>> tile, and have them inheriting from the parent table that the Arkansas NED
>>>>>>>>>>>>> is inheriting from. Ever since, however, my database seems to be running
>>>>>>>>>>>>> pretty slow. I've run a full vacuum on the data, and there are constraints
>>>>>>>>>>>>> on each table.
>>>>>>>>>>>>>
>>>>>>>>>>>>> How can I be sure that when I query the parent database that
>>>>>>>>>>>>> it's not querying every single table?
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 3:14 PM, Bborie Park <
>>>>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> I'm just glad to help. Feel free to post your experience,
>>>>>>>>>>>>>> feedback, issues and/or wishes on the mailing-list.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> -bborie
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 1:10 PM, Jayson Gallardo <
>>>>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Oh, okay. Yeah you're right about it taking time. I wrote a
>>>>>>>>>>>>>>> python script to generate the raster2pgsql call with the appropriate table
>>>>>>>>>>>>>>> name, so I can just let it run while I do other things. I really appreciate
>>>>>>>>>>>>>>> your help on this. I googled your name and I see you're a pretty busy
>>>>>>>>>>>>>>> person, so I'm glad you're taking the time to answer my questions.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 3:05 PM, Bborie Park <
>>>>>>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> No. I'm suggesting it later as it does take time and
>>>>>>>>>>>>>>>> separates operations. Get everything imported first and then add
>>>>>>>>>>>>>>>> constraints.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Having said that, you can do it all at once if so
>>>>>>>>>>>>>>>> desired... just preference depending on volume of import data.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> -bborie
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 1:02 PM, Jayson Gallardo <
>>>>>>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Okay, is there a specific reason why? As your link states:
>>>>>>>>>>>>>>>>> "raster2pgsql loader uses this function to register
>>>>>>>>>>>>>>>>> raster tables". Are you saying I should specify constraints that will be
>>>>>>>>>>>>>>>>> similar across all tables?
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 2:53 PM, Bborie Park <
>>>>>>>>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> I'd suggest adding constraints after the fact through SQL
>>>>>>>>>>>>>>>>>> instead of letting raster2pgsql do it.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> http://www.postgis.net/docs/manual-2.0/RT_AddRasterConstraints.html
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> -bborie
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 12:51 PM, Jayson Gallardo <
>>>>>>>>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> So based on the link you provided, and what else I've
>>>>>>>>>>>>>>>>>>> gathered, I first create a parent table:
>>>>>>>>>>>>>>>>>>>  CREATE TABLE dem_elevation
>>>>>>>>>>>>>>>>>>> (
>>>>>>>>>>>>>>>>>>>   rid integer NOT NULL PRIMARY KEY
>>>>>>>>>>>>>>>>>>>   rast raster,
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> );
>>>>>>>>>>>>>>>>>>>  Then I run raster2pgsql on all the downloaded elevation
>>>>>>>>>>>>>>>>>>> data, sending each input tile to its own table, ie. dem_elevation_n36w091.
>>>>>>>>>>>>>>>>>>> Then alter table to inherit from parent:
>>>>>>>>>>>>>>>>>>> ALTER TABLE dem_elevation_n36w091 INHERIT dem_elevation;
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> With raster2pgsql taking care of setting the constraints
>>>>>>>>>>>>>>>>>>> for each table. Now, I can just query the parent table dem_elevation to get
>>>>>>>>>>>>>>>>>>> what I need?
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 2:33 PM, Bborie Park <
>>>>>>>>>>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> I use the USGS NED 10 meter for California with one
>>>>>>>>>>>>>>>>>>>> table for each input raster. In the partitioned table scheme, data tables
>>>>>>>>>>>>>>>>>>>> inherit from a template (parent) table. Queries run on the parent table
>>>>>>>>>>>>>>>>>>>> access the inherited tables.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> -bborie
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 11:56 AM, Jayson Gallardo <
>>>>>>>>>>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> Yes, it's usgs ned. And I initially went with one
>>>>>>>>>>>>>>>>>>>>> table for each input tile, but I didn't know how to join (or union) them
>>>>>>>>>>>>>>>>>>>>> together for my query.
>>>>>>>>>>>>>>>>>>>>>  On Jul 23, 2013 1:14 PM, "Bborie Park" <
>>>>>>>>>>>>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> Can you describe your elevation dataset? Is it USGS
>>>>>>>>>>>>>>>>>>>>>> NED? At which resolution (10 meter, 3 meter?)?
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> As for table partitioning...
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> http://www.postgresql.org/docs/9.0/static/ddl-partitioning.html
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> You'll probably partition spatially, though an easy
>>>>>>>>>>>>>>>>>>>>>> solution is to have a table for each input raster file.
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> -bborie
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 11:05 AM, Jayson Gallardo <
>>>>>>>>>>>>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> Thanks for responding. Could you outline how I would
>>>>>>>>>>>>>>>>>>>>>>> go about doing a partitioned table structure? My only concern with tile
>>>>>>>>>>>>>>>>>>>>>>> size is processing time. Most of my queries will involve areas of less than
>>>>>>>>>>>>>>>>>>>>>>> 1 mi^2, and I would clip the data into that shape. I just don't know where
>>>>>>>>>>>>>>>>>>>>>>> to start! There's not too many resources online/print dealing with postgis
>>>>>>>>>>>>>>>>>>>>>>> rasters in detail.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 12:57 PM, Bborie Park <
>>>>>>>>>>>>>>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> You may not need to drop all the constraints when
>>>>>>>>>>>>>>>>>>>>>>>> adding additional data to the table. You most likely will need to drop is
>>>>>>>>>>>>>>>>>>>>>>>> the maximum extent constraint. Assuming the input rasters have the same
>>>>>>>>>>>>>>>>>>>>>>>> scale, skew and SRID as that found in the table, you don't need to drop
>>>>>>>>>>>>>>>>>>>>>>>> those corresponding constraints.
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> If you're going to do the continental US at a fine
>>>>>>>>>>>>>>>>>>>>>>>> resolution (e.g. 1 meter), you do NOT want to put all the rasters in one
>>>>>>>>>>>>>>>>>>>>>>>> table. You'll want to use a partitioned table structure and should consider
>>>>>>>>>>>>>>>>>>>>>>>> a bigger tile size (depending on your hardware).
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> -bborie
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> On Tue, Jul 23, 2013 at 10:43 AM, Jayson Gallardo <
>>>>>>>>>>>>>>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>> I've looked and looked, but I have not been able
>>>>>>>>>>>>>>>>>>>>>>>>> to find an answer to my question. I have downloaded elevation data for the
>>>>>>>>>>>>>>>>>>>>>>>>> state of Arkansas (in the form of multiple tiles), and used raster2pgsql to
>>>>>>>>>>>>>>>>>>>>>>>>> upload it into a single table:
>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>> raster2pgsql -I -C -e -F -t 50x50 -l 2,4 n*/grdn*
>>>>>>>>>>>>>>>>>>>>>>>>> public.dem_elevation | psql -U postgres -d testdb -h localhost -p 5432
>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>> I did this because I didn't know how to pull the
>>>>>>>>>>>>>>>>>>>>>>>>> data if they were in separate tables. Now, however I would like to add
>>>>>>>>>>>>>>>>>>>>>>>>> elevation data for other areas. I tried to just add it to the current
>>>>>>>>>>>>>>>>>>>>>>>>> table, but that required dropping the constraints which for such a huge
>>>>>>>>>>>>>>>>>>>>>>>>> amount of data seems to take a long time (I let it run for 24+ hours and it
>>>>>>>>>>>>>>>>>>>>>>>>> didn't finish). So, my question is, if I load all my rasters as individual
>>>>>>>>>>>>>>>>>>>>>>>>> tables, how could I run something similar to this query on them all (from a
>>>>>>>>>>>>>>>>>>>>>>>>> python script):
>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>> SELECT ST_AsGDALRaster(ST_CLIP(ST_Union(rast),
>>>>>>>>>>>>>>>>>>>>>>>>> ST_GeomFromText(WKT,900913)),'GTiff') FROM "dem_elevation" WHERE
>>>>>>>>>>>>>>>>>>>>>>>>> ST_Intersects(rast, ST_Transform(ST_GeomFromText(WKT,900913),4269))
>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>> My goal, if it's not obvious, is to clip elevation
>>>>>>>>>>>>>>>>>>>>>>>>> data and export it to a GTiff format and perform some operations on that
>>>>>>>>>>>>>>>>>>>>>>>>> raster data. Eventually, I would like to put the whole continental US
>>>>>>>>>>>>>>>>>>>>>>>>> elevation data into my database, so I need to be able to do so, while still
>>>>>>>>>>>>>>>>>>>>>>>>> being able to query them based on an area of interest the user selects from
>>>>>>>>>>>>>>>>>>>>>>>>> a map. I started working with PostGIS and Mapserver last month, so please
>>>>>>>>>>>>>>>>>>>>>>>>> forgive my ignorance on such topics. Thanks in advance
>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>>>>>>>>>>>>>>> postgis-users mailing list
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>>>>>>>>>>>>>>>>>>>>>>>>>
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>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>
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